Yumi

Yumi

So, I am making another yumi and decide to take some photos.
Well, I have split my bamboo before taking photo, so, look at this diagram instead.

This is how you split. A side is side where branch comes out and B side is side of bamboo. Sometimes there are no branch to show which side is which, so, you
must pay close attention to profile, which I will show later. Best to use the A sides for the bow, as they will be straight. B sides can be used, but you will
see they need to be straightened!

Here are the bamboo splits.

A side is on the left and B is on the right. There is clear difference between the two.... I hope!

After you split, inner node walls need be cut off.

Well, I will show the flattening process later~
Dimensions at this point, about 45 mm wide, 5 mm thick and 230 cm long. I will take it down to 227 cm later for backing and 197 cm for belly.

Marking out the core to be sawed.

I dont know if there is western tool like this, but it is quite handy for marking boards. I am giving apitong another try, this board is springier than other I
try, maybe it has some potential. Thickness at this point is 10 mm, which will be planed to 8 mm and tapered. No bamboo in this core, dont have enough right
now. so this may be little heavier in mass, its ok though.

This is the wood I use for the tips. Top one is 178 mm and bottom is 127 mm. Both are 28 mm wide.
Though it looks quite grey, the wood is actually brighter red, bad lighting. It is Bischofia javanica wood, not too heavy but hard enough for this
purpose. Since this is test bow, I use this wood intead of ebony. I will also coat with red finish so wood color doesnt really matter anyway.

All that is needed, backing/belly, core, tips. Just the glue is not included here, which I will use modern glue for my convenience. I dont think hideglue is
good choice since apitong is quite sappy wood.

Ok, finish flattening bamboo.
Core was still quite wide at this point， so I shave down to 32 mm.

Also, If you ever use this wood for some reason, or similar type with much sap, beware for your blades will be nasty after!

Well, I use simple process to flatten bamboo. You need make sure your tool blades are very sharp though, it makes for more precise work indeed. Easier to cut
through the node joints as well! The wood block plane is main tool and other is drawknife. I just use a wood stock to lay bamboo on, this give it flat surface
and give some stiffness (?) because it will soon become very flexible.

Ok, now we shave until we have edge on both side.

After it has been shaved down, use the core to draw out lines to cut to width as shown above.
It should look like this. After you have shaved down the side, again, shave thickness until you have edge and it should be flat now.

note: Make sure you use a bamboo pole with minimum diameter of 6.5 cm, any smaller and it becomes difficult to have good
width and flat surface when flattening.

The backing plate is 5 mm thick in the handle area and tapers to 3mm at the top and 2 mm at the bottom. The belly is 5 mm the whole length and both are 32 mm
wide at this point.

Next I will shape the nock pieces into slight curve and square up to be glued.

Nick, I may do rope/wedge method if I can make some more wedges. If not, I will just post later on it. I only have 28 wedges, I need 120 to glue a yumi so we
see what can be done.

I did not see squares, but I think I know problem, it is fixed now?
Always forget to switch back to American english format when typing~

Ok well just a reminder for people new to bamboo, be careful of the sharp edges it may produce.
The are sharp indeed!

Well, I got the nock pieces cut to the curvature. You only need slight curve, this is so it may smoothly transit from the main curve on the top and bottom limb
when it is glued.

As you can see, these are still quite bulky in size, they are maybe 3x as thick as I need, but this allows me to have peaceful mind to carve, not much worry
about mess up~
I went ahead and glued on the nock pieces since I lack number of wedges. Usually you glue it on same time as the other pieces.

The black line is pencil mark I forget to scrap off~

note: When making core, make sure to taper last length (about sive of nock piece) to 1.5~2mm thickness at end. It will help
it bend easier to curvature.

Commonly used woods for the nock piece are mulberry, rosewoods, ebony, cherry and peach.

Seems I have not explained core configuration much, well let me go into that.
The typical core is made in the higoyumi style these days. This consists of 5 bamboo and 2 wood . All the bamboo is
tempered to black color and wood is left untempered. The wood is left wider, so it may have excess material for stock removal later. Each bamboo is about 4 mm
wide and wood is maybe 8 mm wide. Final width is anywhere from 24~29mm. The core configuration I use here is called sanmaiuchi and it was used during late Heian Period in 12th century.

The type of wood used most comonly for core these days is hazenoki or Rhus succedanea. Others I
have heard of used are mulberry and catalpa, though I have only heard once of use of the catalpa wood. Really, most any bowwood will work for this, but it is
best to use wood the the characteristics of these which are light weight, brittle and springy. Woods I would recommend as good core woods are cherry, plum,
jatoba, padauk, black locust, maple and black walnut. Most yumi makers try to find wood with interesting grain like birds eye, flame or curly so that it may
show in final product. This looks really cool when a dark red urushi finished is applied and you may see how the light reflecs off the wild grain patterns. You
may find this in the maple and walnut wood more easily than the others however.

Some extra information.
When deciding length of yumi, you must first establish your arrow length.
Arrow length is measure from center of your throat to the tips of your extended arm. Add 3-6 cm extra or about four fingers width. Beginners should add extra
10 cm in case of over draw.

Namisun is 221 cm long for 83~88cm arrow
Nisun-nobi is 227 cm long for 88~91 cm arrow
yonsun-nobi is 233 cm long for 91~94 cm arrow

This is from kyudo book I own, though different places say different length. If you do not fall in the categories above, look here http://www.kyudo.com/bowlength.gif
Beginners should start with light weight in 20~30# and more experienced may use weights of 40~50#.

Also, be very careful on thickness of your core. Depending on density of your wood, sometimes it must be thicker or thinner to achieve right strength. I am
expecting a pull of ~40# but I may end with 30~55. I am not experienced enough to know just by thickness yet. My core is same thickness as core on 40# yumi I
examined, however, I use solid wood core which may prove to be much stiffer.....
Old war yumi must be very powerful indeed. My core is only 8 mm thick, though, core of warbow yumi I saw at Sanjusangendo has core thickness of ~18 mm. It must be well over 100#. There are still a few small groups in Japan that practice
mainly on shooting heavy weight yumi in 130# draw weight so we can expect that a yumi in old days must have been very powerful.

I decide to do rope and wedge glue up, so we shall wait a bit until I finish all.....120 wedges.
Some how I will try to get pictures of this, though maybe not pictures during the process or maybe I can take video? hmmm....

Thank you Thimo!
Ah, I remember that well, I hope it has healed well by now?

Nick,
The style of drawing a yumi is very unique. The wrist is not bent like with western style shooting, but straight like when holding sword. In this case, we have
stronger wrist. Another strength is you are inline with draw force. I will have to get picture to show what I mean, but you are inside the bow when pulling,
the string is almost behind your head, making the weight lay on the structural frame of your body instead of on your sinews alone. This, with the high draw
starting with a push and then letting down with a pull creates a very solid way to pull the bow. Only weakness is in the draw wrist which is not straight, but
it is possible to over come this~ I think this is reason for their ability to draw mighty bow.

thanks for your info Mr Kinjo!
really interesting. But I've seen many pictures of yumi archers, and it seemed they pulled their bows mainly with their triceps, wich is pretty hard... But
I'll take another look. This is indeed very eductional!

Alex! I tend to donate a fair amount of blood to the bamboo I use as well. I think its good mojo.. Very interesting thread. I remember seeing a very skilled
Japanese Yumi bowyer do a glue-up in a documentary about 20 years ago, and I learned a ton from this since it was when I was doing my first laminated bows.
They probably have the sharpest tools going..

I bet if you put a 3/8th" core of that Ipe in one of those bows it will make the arrow happy..I have one thick pole set aside for this style of bow..

Ok not much time to reply as I leave soon so sorry but I will reply to your comments when I return.

I just wanted to give notice that I wont ever use the titebond glue for this work again.
It is good glue, just, the working time is much too short!
I end up with only 20 cm reflex...well, I will try to see if it still will work, just a bit slower bow.

Really, you want around 40 cm reflex and end with 15~25 cm. If the bow had been shorter titebond may have been fine but not with 227 cm bow!
I think, depending on final brace shape I may consider glue backing again by removing with heat.
At this point, I think shape will be close to old yumi, less recurved tips and more round shape at brace.

This is a super awesome thread, Alex, very interesting and educational indeed. I love seeing the pics of your tools, as well as the bow coming together. The
one you used to mark your core would be called a marking gauge, I use one that works the same although a bit different in detail. What is it called in
Japanese?

Ichi,
Thanks, I will add more info after the build on core designs and other techniques so it may be easier to make.

Hey Rich,
Yeah, with the amount of bamboo you use, I am sure of it!
I wonder if this man you talk about is Shibata Kanjuro XX ? He is the master yumi bowyer of Japan.

hah! If I put that ipe in there I may not be able to pull! Though, I think indeed it may work very well.
Maybe you can experiment with that on you're yumi.

Thanks Orien!
Maybe I will get a group picture of all the tools and place it at the beginning of thread.
Ah, I did not know you have one too! neat!
Well, in Japanese it would be kamakebiki, Kebiki is the name for marking guage and kama describes the type of blade. This is for mortise and tenon work. If it
was Warikebiki it is for splitting thin wood. Wari means split, it is not full metal, but has wooden arm and a blade at the end.

It does not need a long taper. These wedges are 15 cm long and have taper around 6 cm or so.

Now for the wrapping!
I just use some vinyl rope I had at hand, but usually I use hemp rope. The vinyl is nice though because it wont stick to the bow, but it lasts only one wrap
because it often cuts from the wedge.

First, you want to spread the glue on all surfaces very fast, make sure it is not thin either. You can use some wood to spread so fingers dont get sticky.
After surfaces are prepared, put pieces together and tape in three places, upper tip, middle and lower tip.
Now wrap the bow leaving space of maybe 1 inch whole way, then wrap back crossing over first wrap.

Start inserting wedges from the top limb up. If you put the wedges on the back of the nock piece area it is easer to continue the other side.
After you have inserted enough wegdes to clear the nock piece, start inserting on the belly side immediatly after nock piece. Continue for about a foot and
half length. While holding the bow in your left hand (or right) use your foot to push against the back of the bow, this loosens the wedges so they may be
driven deeper with your other hand. You should have a strong reflex now on the top limb.

Next insert wedges on the back for another foot and a half. Repeat same process of bending and pounding the wedges, only this time do not put much curve! Just
maybe 1~2" of deflex is fine. After this, start wedges on belly again until you pass the handle. Again, strong reflex here.

Contine with wedges on the back for a foot and deflex 1~2" then wedges on the belly and reflex the bottom tip.
Go back and pond in any loos wedges and make sure they are straight or they will loosen. You should have 45 cm or reflex.
This must all be done before the glue sets so work fast!

Tip: to do this fastly,you should put in the wedges for reflex first, which is easily done with careful marking of the bow
for wedge placement. Since these must be bent the greatest it is good to do these first befor the glue sets, then do the deflex wedges since they need little
bend.

After it has cured, remove wedges/rope. I use the marking tool to mark final width after I remove the excess glue.
You should keep it slightly wider first. If it is too strong in one area, you may shave it more. The belly is slightly less wide than back so keep this in mind
while correcting tiller.

When you are satisfied with the width, start bending the bow in different areas to teach to bend. Mostly in deflexed areas, then hold handle
and bottom tip and bend top limb. Flip around and repeat. There is special form to do this, I will see if I can post a picture later. I dont have one so I will
look on japanese website.
(The bow needs repair as the glue let go. I just wait for it to cure then I continue the tiller. Indeed, it feels much slower than other, put in that 45 cm
reflex!)